This invention relates to a release agent for die casting with a superior lubricating property which may be used for die casting of aluminum alloys, magnesium alloys, zinc alloys and the like.
Silicone oils have been used as a representative component for a water-soluble release agent for die casting. Particularly, alkyl-modified silicones such as xcex1-olefin-modified silicone, xcex1-methylstyrene-modified silicone, phenyl-modified silicone and carboxy-modified silicone have been widely used in actual working, because the alkyl-modified silicones may provide a superior release property due to the lubricating property of the alkyl group and a hard release film formed on die by gelling on heating.
Dimethyl silicone, which is also one of silicone oils, is a highly stable compound and therefore has heat resistance, whereby a solid film is not formed on die of die casting. As a result, it has drawbacks of poor release property and lubricating property. Moreover, it may significantly impair painting property of cast products. Consequently, it has never been recognized as a release agent for die casting, nor has it been applied for actual working.
Although alkyl-modified silicones could exhibit a superior release property in a lower temperature range, they tend to be decomposed and vaporized at an elevated die temperature of above 300xc2x0 C. so that a sufficient release property could not be maintained. Thus, there has been a demand for improvement of their release property at an elevated temperature.
An object of this invention is to provide a release agent for die casting which may exhibit a superior lubricating property or a release property not only in a low-temperature die but also in a high-temperature die.
The present inventors have paid the attention to dimethyl silicone, which has never attracted interest because of its difficulty in use, and brought to completion of the present invention based on the finding that the above object may be achieved by using the said silicone together with alkyl-modified silicones widely used in the prior art.
More specifically, this invention is directed to a release agent for die casting, which is an aqueous emulsion comprising 5-50% by weight of a silicone mixture containing dimethyl silicone and an alkyl-modified silicone, 0.5-5% by weight of a surfactant, and water.
The invention is also directed to the said release agent characterized in that a mixing ratio of said dimethyl silicone to said alkyl-modified silicone is 5:1-1:5.
The invention is further directed to the said release agent characterized in that dimethyl silicone has a kinematic viscosity of 200-5000 cSt at 25xc2x0 C.
Moreover, the invention is directed to the said release agent characterized in that the said alkyl-modified silicone has an alkyl chain of 6-18 carbon atoms, a modifying rate of 50-100%, and a kinematic viscosity of 200-5000 cSt at 25xc2x0 C.